Diet and Colon Cancer Prevention Nancy D. Turner Nutrition & Food Science Department Faculty of Toxicology Faculty of Genetics Vegetable and Fruit Improvement Center Texas A&M University College Station, TX

Overview of Talk  Quick review of colon cancer  Evidence from our lab  Discussion of potentials/pitfalls in use of phytochemicals  Summary

What is Carcinogenesis  Multistep process  Cellular  Molecular  Typically takes many years to develop  Colon cancer can take up to 40 years

Stages of Carcinogenesis  Initiation  Exposure to carcinogenic agents  Changes at the DNA level - selective growth advantage  Promotion  Expansion of initiated cells  Progression  Tumors  Metastasis

Normal Growth and Function  Cell number determined by  Proliferation  Apoptosis  Cell phenotype determined by  Differentiation

Normal Colon Architecture Epithelial cells Goblet cells Proliferation Differentiation Apoptosis

Cancerous Growth  Loss of cell cycle controls  Increased proliferation  Decreased apoptosis  Results from  Genetic changes - mutations/deletions  Epigenetic changes - altered gene expression

Cartoon of Cancer Development Proliferation Apoptosis

Genetic Changes  DNA is damaged by exogenous and endogenous:  Reactive oxygen species  Reactive nitrogen species  Alkylating agents  Lipid peroxidation products

Exogenous vs Endogenous  Exogenous sources of oxidants and carcinogens are found in the diet  Component of food  Result of food processing/cooking  Endogenous sources derived from metabolism  Conversion of pro-carcinogens to ultimate carcinogen  Reactive oxygen species generation

Chemoprevention Opportunities  Reduce formation/uptake of carcinogens  Modification of carcinogen metabolism  Scavenge activated carcinogens  Inhibit DNA adduct formation  Antioxidant activity  Cell cycle activity regulation  Normalize cellular signal transduction

Epidemiological Results  Cancer prevalence is higher in cultures where intake of plant-foods is low  Cancer incidence increases as people migrate from low to high incidence rate environments  More of an effect of environment (e.g., diet) than genetic predisposition

Questions on Colon Carcinogenesis  Chemicals that promote colon cancer are derived from….?  Cancer growth differs from normal growth in what ways?  What are the stages of carcinogenesis and what characterizes the events of that stage?

So What Is in the Diet that Can Protect Us from Colon Cancer?

Quercetin  Quercetin is present in many plant-based foods  Level depends on food source  High plant food diets would provide a reasonable mass of the compound

Quercetin Inhibits Colon Cancer  We demonstrated  Reduction in early colon cancer lesions  Proliferation and apoptosis effects  Lower expression of COX-1, COX-2 Warren et al., 2009; J. Nutrition 139:101

Quercetin Conclusions  Suppresses development of early lesions  Beneficially affects proliferation and apoptosis to return cell numbers to normal levels  Has a small impact on pro- inflammatory mediators

Flavonoids and Limonoids  Citrus contains many different compounds with potential  Evaluated relative protection in 5 diets  Basal  Rio Red grapefruit pulp powder (GFPP, ~1.5/day)  Irradiated Rio Red grapefruit pulp powder (IGFPP)  Isolated Naringin (same level in GFPP)  Isolated Limonin (~10-15 times higher than GFPP, but same level as Naringin)

Early Lesions P = 0.01 b b b a HMACF Number (% of Basal) All diets reduce formation of these early lesions. b Vanamala et al., 2006; Carcinogenesis 27:1257

Proliferative Index P = 0.02 a b b b b Proliferative Index (% of Basal) All diets reduce proliferation with the maximum reduction occurring with the GFPP and limonin diets.

Apoptotic Index P = 0.02 a bb c c Apoptotic Index (% of Basal) The GFPP and limonin diets caused the greatest level of apoptosis

Mechanisms?  Colon cancer is promoted by repeated bouts of inflammation.  Reducing proinflammatory proteins may be protective

Cyclooxygenase - 2 COX-2 Protein Level a a b b ab P < COX-2 levels were lowest in rats consuming the GFPP and limonin diets.

What About Other Citrus Compounds  Not all compounds perform equally  Naringenin and Apigenin reduce early lesions  Naringenin reduced proliferation  Naringenin and Apigenin increased apoptosis Leonardi et al., 2010; Experimental Biology & Medicine 235:710

Conclusions for Citrus Flavonoids/Limonoids  Grapefruit and some bioactives reduce colon carcinogenesis  Not all citrus compounds have equal protective ability  Irradiation may negatively affect the chemoprotection provided by grapefruit.

Inflammation  Inflammation promotes colon cancer  Can bioactive compounds inhibit chronic inflammation and injury  Stonefruits  Bran from grains

Inflammation-Induced Injury

Activation of NF-  B

Intestinal Microbiota and IBD  Intestinal bacterial populations (dysbiosis) are tied to development and severity of colitis  Recurrent colitis is a promoter of colon cancer

Colon Microbial Differences Distinct diet patterns Brans contain Anthocyanidins (black) Condensed tannins (sumac) Both (high tannin) CelluloseBlackSumacHigh Tannin Ritchie, Azcarate-Peril, and Turner, In Preparation

Inflammation and Injury Induction  Black and Sumac sorghum reduced activation of an inflammatory mediator (NF-  B) and resulting injury scores p=0.01, R 2 =0.98 Ritchie et al. (unpublished data) Black Cellulose Sumac High-Tannin Black Pectin

Inflammation Conclusions  During chronic inflammation, injury and inflammation induction are dependent on fiber type  Activation of NF-  B (inflammation regulator) is lowest in rats consuming chlorogenic acid or brans from black or sumac sorghums  Diet has a major impact on microbial populations

Interactions Between Substances  Studying a molecule in isolation ignores potential interactions with other diet components.  One molecule may affect absorption/ availability of another (ß-carotene reduces absorption of other carotenoids)  Compounds may oppose or enhance effects of other compounds

Prevailing Wisdom  Insoluble fiber more protective  Fish oil (omega 3 fatty acid source) would be protective  Hypothesis:  Combination of fish oil and cellulose would reduce tumor incidence

Fat and Fiber in Colon Cancer Rats with Colon Tumors, % a a,b b Chang et al., 1997; Carcinogenesis 18:721

Human Studies Suggest Caution  In both the ATBC and CARET trial - ß-carotene promoted lung cancer  Dietary recommendations, or “treatments”, need to be tailored for the individual, not the population  Recommendations for someone without the disease or in the early stages may differ from those for someone with cancer  Vitamin E and prostate cancer trial (SELECT) was also stopped because of enhanced cancer rates

Supplement vs Functional Food  Supplements  Bolus of compound  Usually in a purified form  Functional food  Smaller amount of compound  Slows delivery  Competes/complements other molecules present in food

Is it Always a Chemoprotectant?  Although a molecule may protect against a certain type of cancer, it is not always beneficial to all systems  Need to evaluate multiple mechanisms  Need to study a variety of tissues/diseases  Will require more data  How does processing affect responses

Summary  Many potential chemoprotectants  More work is needed to identify individuals in populations that will benefit  Must be aware of potential interactions  Functional foods probably more desirable than nutraceutical supplements

Bioactive Questions  Are all bioactive compounds effective at preventing colon cancer?  What are the possible mechanisms of chemoprotection conferred by bioactive compounds?  What are the pros and cons of using a supplement vs getting compounds via the food?